Rates of formation, of destruction and of mineralization of elementary volumes of bone will be determined in weanling rats during recovery from hypovitaminosis A and hypervitaminosis A by a combination of calcium kinetic and balance studies with separation by density gradient. BIBLIOGRAPHIC REFERENCES: Morphological alterations associated with decreased cerebrospinal fluid pressure in chronic bovine hypervitaminosis A (1975), Amer. J. Vet. Res., 36(2): 171-180, E.J. Gorgacz, S.W. Nielsen, H.I. Frier, H.D. Eaton and J.E. Rosseau, Jr. Cerebrospinal fluid pressure and squamous metaplasia in chronic hypovitaminosis A of the male weanling rat (1975), Storrs (Conn.), Agr. Exp. Sta. Res Rpt., no. 46, 68 pages, H.I. Frier, R.C.Hall, Jr., J.E. Rosseau, Jr., H.D. Eaton and S.W. Nielsen. Effect of vitamin A on calcium metabolism in the weanling rat. (1975), Fed. Proc., 34(3): 937, H.I. Frier, L.J. Richelle, J.E. Rosseau, Jr. and H.D. Eaton (Abstract). Bone growth in the hypo- and hypervitaminotic A male weanling rat (1975), Ph. D. thesis, Graduate School, University of Connecticut, H.I. Frier.